Stereoscopic Light Recycling Device

ABSTRACT

A stereoscopic device for recapturing light is provided. A chassis is open on front and back sides and forms a rectangular housing with top, bottom, and two sides that frame the front and back openings. A polarizing beam splitter is angled away from the back opening of the chassis and captively held by the chassis. The beam splitter is constructed of substantially orthogonally polarizing material. A phase shifting optic having a reflective surface coated by a phase shifting film is angled toward the front opening, wherein the beam splitter and phase shifting optic are in optical alignment with each other within the chassis. A modulator sized to cover the front opening is positioned in front of the chassis.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional patent application claims priority under 35 U.S.C.§119(e) to U.S. Provisional Patent Application Ser. No. 61/805,457,filed Mar. 26, 2013, the disclosure of which is incorporated byreference.

FIELD

The invention relates in general to stereoscopic imaging, and inparticular, to a stereoscopic light recycling device.

BACKGROUND

Since the mid-1980's, three-dimensional (3D) films have greatlyincreased in popularity worldwide. 3D films enhance an illusion of depthperception, such that images in the film can appear to a viewer toextend in and out of a projection screen. Stereoscopic imaging devicesare commonly used for playing 3D films, and in the past, have utilizeddual projection systems with passive polarization. However, currentstereoscopic imaging devices now utilize a single digital projectionsource combined with an active polarizing modulation device. Forexample, the single digital projection source can alternately projectright and left eye frames. The active polarizing modulation device thenalternately polarizes each frame using linear or circular polarization.Viewers wear glasses with oppositely polarized lenses to experiencethree-dimensional features that appear to extend in and out of apolarization-preserving projection screen.

However, while offering substantial quality benefits in comparison withdual projection systems, stereoscopic imaging devices with a singleprojection source emit images with substantially reduced brightness.Specifically, the light from a projection source must be linearlypre-polarized for the polarization modulating device to function. Otherfactors that contribute to the loss of light include the duty cycle ofthe projected left and right frames, dark time, white point calibration,reflective and transmissive surface losses, and polarizationinefficiencies.

Attempts to increase image brightness of current stereoscopic imagingdevices have been made. For instance, U.S. Pat. No. 7,857,455, to Cowan,discloses a multiple path stereoscopic projection system to enhancebrightness of stereoscopic images perceived by a viewer. The systemincludes a polarizing splitting element, a reflector, a retarder, and apolarization modulator. Light received by the stereoscopic projectionsystem is split into a primary path and a secondary path. The reflectorand retarder are typically located in the secondary path, while thepolarization modulator is located within at least the first path. Thestereoscopic projection system includes multiple parts withexposed-to-air surfaces that can be difficult to clean, and which canreduce the quality and brightness of the images and the lifespan of thesystem if left uncleaned. Therefore, a stereoscopic imaging device withfewer parts and exposed surfaces is beneficial to maintain image qualityand increase the life of the device.

Further, U.S. Pat. No. 7,905,602, to Schuck, discloses a polarizationconversion system that is located in a randomly-polarized light pathemitted by a projector. The polarization conversion system includes apolarizing beam splitter, a polarization rotating element, a reflectingelement, and a polarization switch. The beam splitter separates p- ands-polarized light. The p-polarized light is directed on a first path tothe polarization switch, while the s-polarized light is directed on asecond path, passed through the polarization rotating element andtransformed to p-polarized light before reaching the reflecting elementwhich directs the now p-polarized light to the polarization switch.Additionally, the conversion system includes a telephoto lens pair tocontrol magnification, distortion, and imaging properties of the firstlight path. The numerous parts and exposed-to-air surfaces of thepolarization conversion system can be difficult to clean and expensiveto maintain. However, without cleaning and maintenance, the quality andbrightness of the images deteriorates and the life span of theconversion system is reduced.

Currently, a polarization conversion system with fewer parts and exposedsurfaces is needed to increase quality and brightness of stereoscopicimages while decreasing maintenance and increasing the life of thesystem.

SUMMARY

A stereoscopic light recycling device increases the brightness of imagesprojected from a single projector. The light recycling device includes abeam splitter and phase shifting optic, which are both housed within achassis, and a polarizing modulator. The chassis is placed in front ofthe projector, while the polarizing modulator is placed in front of thechassis, opposite the projector.

One embodiment provides a stereoscopic device for recapturing light. Achassis is open on front and back sides and forms a substantiallyrectangular housing with top, bottom, and two sides that frame the frontand back openings. The open back side can be enclosed by a back coverthat includes at least one opening or aperture to allow light to enterthe chassis. A beam splitter is angled away from the back opening of thechassis and captively held to the chassis. The beam splitter isconstructed of substantially orthogonally polarizing material(s). Aphase shifting optic having a reflective surface coated by a phaseshifting film is angled toward the front opening, wherein the beamsplitter and phase shifting optic are in optical alignment, orsubstantially facing each other within the chassis. A polarizingmodulator is positioned in front of the chassis and sized to receive allthe light from both the beam splitter and the phase shifting optic.

Still other embodiments and applications will become readily apparent tothose skilled in the art from the following detailed description,wherein are described embodiments by way of illustrating the best modecontemplated. As will be realized, other and different embodiments arepossible and their several details are capable of modifications invarious obvious respects, all without departing from the spirit and thescope. Accordingly, the drawings and detailed description are to beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an environment for a stereoscopiclight recycling device.

FIG. 2 is a block diagram showing, by way of example, a light converterfor use in the recycling device of FIG. 1.

FIG. 3A is a block diagram showing the phase shifting optic of FIG. 2.

FIG. 3B is a cross-sectional view of the phase shifting optic of FIG. 2.

FIG. 4A is a block diagram showing an adjustable phase shifting optic ofFIG. 2 moveably connected to the chassis.

FIG. 4B is a cross-sectional view of the adjustable phase shifting opticof FIG. 2.

FIG. 5 is a block diagram showing a back side of the light converter ofFIG. 2.

FIG. 6 is a block diagram showing an alternate light converter for usein the recycling device of FIG. 1

FIG. 7 is a block diagram showing a side view of the recycling device ofFIG. 1.

FIG. 8 is a block diagram showing a front view of the recycling deviceof FIG. 1.

FIG. 9 is a block diagram showing, by way of example, light transmittedthrough the recycling device of FIG. 1.

FIG. 10 is a block diagram showing the light converter of FIG. 6 with afixed focal length lens.

FIG. 11 is a block diagram showing the light converter of FIG. 6 with atelephoto lens pair.

FIG. 12 is a block diagram showing light transmitted through therecycling device of FIG. 1 with a four-prism cube beam splitter.

FIG. 13 is a block diagram showing light transmitted through therecycling device of FIG. 1 with two beam splitters and two phaseshifting optics.

FIG. 14A is a ray trace showing, in one example, light reflected awayfrom the static phase shifting optic of FIG. 6 and illustrating auniform surface shape.

FIG. 14B is a ray trace showing, in one example, light reflected awayfrom the adjustable phase shifting optic of FIG. 2 adjusted to create anon-uniform surface shape.

FIG. 14C is a ray trace showing, in one example, light reflected awayfrom the static phase shifting optic of FIG. 6 and illustrating anon-uniform surface shape.

DETAILED DESCRIPTION

Traditionally, a stereoscopic display system required two separateprojectors, which each projected a slightly different perspective of acommon image. However, conventional stereoscopic display systems now usea single projector with a polarizing modulation device to alternatebetween both perspectives. The alternating perspectives from a singleprojector eliminate alignment and other asymmetry problems, includinggeometry, color, white-balance, brightness, and timing that areassociated with the traditional display system, making the conventionalsystems far more comfortable to view, easier to maintain, and much moredesirable. A disadvantage of the conventional systems versus thetraditional systems is a loss in image brightness, not only due to theloss of one of the projectors, but also from factors including the dutycycle of projected left and right frames, pre-polarization of incominglight, dark time, white point calibration, reflective and transmissivesurface losses, and polarization inefficiencies.

Conventional systems that attempt to increase the brightness ofstereoscopic images from a single projector include many opticalcomponents with multiple surfaces exposed to air that must be thoroughlycleaned and maintained to receive the benefits of the increasedbrightness. Stereoscopic display systems are typically operated incommercial theater environments which include food preparationparticulates in the air, especially popcorn oils. This fine, stickyparticulate coats optical surfaces and subsequently draws other dust andparticulates, and is a commonly reported issue in the industry. Thecleaning can be difficult and time consuming, but if left undone, candecrease the image quality and reduce a lifespan of the device.

The stereoscopic light recycling device can be used with a projector toincrease brightness of 3D images projected by the projector, whileincluding only minimal components and exposed-to-air surfaces to reducemaintenance and maintain image quality, brightness, and device life.FIG. 1 is a block diagram showing an environment for a stereoscopiclight recycling device 13. A projector 11 is positioned near a back of aroom, while a polarization-preserving projection screen 12 is placed ata front of the room opposite the projector 11. The projector 11 can be athree-chip projector that splits light received into red, green, andblue colors, which are separately directed to three digital micromirrordevice chips and subsequently recombined. Other types of projectors arepossible. However, at a minimum, the projector should emitpartially-polarized light. In one embodiment, the polarized portionshould be substantially aligned linearly along a vertical axis, with thestereoscopic recycling device optimized for this orientation. In afurther embodiment, an optic can be used with a projector that does notemit partially-polarized light to create the partially-polarized light.In a still further embodiment the projector can emit unpolarized light.

The stereoscopic recycling device 13 can include a light converter 20and a polarizing modulator 21, which are described below in furtherdetail with respect to FIGS. 2, 6, and 8. The light converter 20includes a beam splitter and phase shifting optic, and can be positioneddirectly in front of a lens 19 of the projector 11. The polarizingmodulator 21 is positioned on a front side of the light converteropposite the projector. In one embodiment, the polarizing modulator 21is affixed to the light converter 20. However, in a differentembodiment, the light converter 20 and polarizing modulator 21 are twoseparate components. Both the light converter 20 and polarizingmodulator 21 can be affixed to a device mount 18 that allows thecomponents of the recycling device 13 to move closer towards or awayfrom the lens, to the left or right of the lens, and above or below thelens 19. The mount device 18 can be affixed to a stand for the projectoror to the projector itself.

The light converter 20 receives stereoscopic image light from theprojector lens 19 and splits the light into two separate light beamsthat each provide a separate, but similar, stereoscopic image that isdisplayed on the polarization-preserving projection screen 12.Specifically, the two stereoscopic images produced will be slightlydifferent due to a difference in path length that the respective lightbeams follow. Thus, stereoscopic images 16 and 17 must be substantiallyaligned on the screen to generate a quality 3D picture that can becomfortably viewed by an audience. In one embodiment, the images shouldbe aligned within one to two pixels or about 0.1% of the overall image.Other thresholds for image alignment are possible.

A viewer 15 wearing stereoscopic glasses 14 sees a single 3D imageprojected on the screen. However, the single projector source 11provides alternating (time multiplexed) left and right eye views of theimage. While the stereoscopic recycling device orthogonally polarizeseach view, the polarization-preserving screen 12 maintains lightpolarization that reflects back to the viewer, and the glasses provide aseparate image to each eye of the viewer. For instance, passive glassesinclude different polarization lenses for the right and left eyes sothat one image enters the viewer's right eye, while the other imageenters the viewer's left eye. The viewer's brain is then able to combinethe input of the right and left eyes to form a single 3D image withdepth.

The stereoscopic recycling device 13 includes a light converter 20 togenerate and direct to the screen a second, similar instance of aconventional system's time-multiplexed left and right stereoscopicimages emitted from the projector, thus increasing the total brightnessof the stereoscopic images reaching the viewer. FIG. 2 is a blockdiagram showing a light converter 20 for use in the recycling device ofFIG. 1. The light converter 20 includes a chassis having enclosed top 30a, bottom 30 b, left 30 c, and right 30 d sides, while a front 35 andback 36 of the chassis 30 a-d can remain open or can be covered. In oneexample, the open front side of the light converter can be covered bythe polarizing modulator, while the open back side can be enclosed by aback cover that can include at least one opening or aperture to allowlight to enter the chassis. The back cover of the chassis is furtherdescribed below with reference to FIG. 5. In a further embodiment, thefront and back sides can remain open while components within thechassis, such as the beam splitter 31 and phase shifting optic 32 areeach enclosed by a protective housing made from anti-reflection coatedglass or other light-transmissive optical materials to prevent dust anddirt from accumulating. Other materials for enclosing the beam splitterand phase shifting optic are possible, including plastic, metal, carbonfiber or wood designed to hold anti-reflection coated glass or otherlight-transmissive optical materials and create a dust-free spaceallowing light passage. The protective housing can be conformably shapedaround each of the beam splitter 31 and phase shifting optic 32, oralternatively, the protective housing can have a different shape, suchas a square or rectangle.

The chassis can be made from metal, heavy plastic, carbon fiber, wood,or other types of material. In one embodiment, the chassis can form arectangular shape with the left 30 c and right sides 30 d longer thanthe top 30 a and bottom 30 b sides. The bottom 30 b side can beperpendicularly affixed to the left 30 c and right 30 d sides, while thetop 30 a side is affixed to the left 30 c and right 30 d sides at anangle facing the open front side of the chassis. However, in furtherembodiments, other shapes of the chassis are possible, including square,cylindrical, spherical, or polygon shapes. For example, the chassis canhave a polygon shape, where a slope extends from the top side, out andalong the back of the left and right sides to accommodate the phaseshifting optic.

The chassis houses the beam splitter 31 and the phase shifting optic 32.The beam splitter 31 can be positioned on a bottom side 30 b of thechassis at an angle with an input side facing the opening in the backside. In one embodiment, two support members 34 are perpendicularlyaffixed to an upper surface of the bottom 30 b side such that thesupport members 34 are also housed by the chassis. In a furtherembodiment, the support members 34 can be affixed to the inner left andright sides of the chassis. The two support members 34 are positioned toface one another at a distance that is dependent on a size of the beamsplitter 31. For example, the longer the beam splitter 31, the furtherthe distance between the support members 34. In one embodiment, the beamsplitter 31 has a rectangular shape with dimensions of 7.3 inches longand 4.4 inches tall. However, other sizes and shapes of the beamsplitter and the support members are possible, including a circular beamsplitter and a cylindrical support member. The shorter sides of the beamsplitter can be affixed to the support members directly or connected viamounts affixed to the support members 34. The angle of the beam splittercan be a predetermined fixed angle, can be based on placement of thephase shifting optic 32, or can be made adjustable by affixing the beamsplitter to one or more adjustable support members. Examples ofadjustable support members can include a kinematic mount with 2-axisangle adjustment such as pitch and roll, or bar and clamp holdersattached to a post which can be rotated within a post holder affixed tothe chassis. Other examples are possible. In a further embodiment, thebeam splitter, if large enough, can be affixed to the left and rightsides of the chassis directly or via fixed or adjustable mounts.

The beam splitter 31 can be a wire grid polarizing beam splitter thatreceives light from the projector lens and splits the light into twoseparate substantially orthogonally polarized pathways of light. Onelight path is passed through the beam splitter along an original path ofthe light received from the lens, while the other path is reflectedtoward the phase shifting optic 32.

Other types of beam splitters are possible, including but not limited tovarious types of cube beam splitters, including a two-prism cube beamsplitter. For example, the beam splitter can be a four-prism cube beamsplitter that can be used with a reflector to create two equal pathlengths of the light beams generated by the light converter as furtherdescribed below with reference to FIG. 12. In a further embodimentmultiple beam splitters can be used as further described below withreference to FIG. 13.

The phase shifting optic 32 is positioned at an angle above the beamsplitter 31 and faces the front opening of the chassis, in an oppositedirection of the beam splitter. The phase shifting optic 32 can beaffixed to the top surface via screws 33 that can be used to adjust thephase shifting optic, as further described below with reference to FIG.4A. Positioning of the phase shifting optic 32 and beam splitter 31should be in optical alignment, which can be dependent on the surface ofthe phase shifting optic and a distance between the projector andscreen, as described infra.

FIG. 3A is a block diagram showing, by way of example, the phaseshifting optic 32 of FIG. 2. Components of the phase shifting optic arenot drawn to scale and are only provided as an example. The phaseshifting optic 32 can be made from a polarization-preserving reflectivesurface 40 and at least one layer of phase shifting film 42. The phaseshifting film 42 can include quarter wave film, which is provided overat least a portion of the reflective surface and affixed viahigh-transmittance optical adhesive 41. Other types of adhesivesubstances can be used to affix the phase shifting film 42 to thereflective surface 40. In a further embodiment, the phase shifting optic32 can be made from a polarization-preserving reflective surface 40directly coated with a phase shifting material not requiring adhesivesubstances. In all cases, the phase shifting optic 32 functions as asingle optical element with a reduced number of exposed faces todecrease required maintenance and increase device life, as well asincrease quality and brightness of stereoscopic images.

When positioned in the chassis, the reflective layer 40 of the phaseshifting optic 32 is positioned closer to the top side of the chassis,while the phase shifting film 42 is positioned closer to the beamsplitter. FIG. 3B is a cross-sectional view of the phase shifting optic32 of FIG. 2. The figure is merely provided as an example and thecomponents are not drawn to scale. Optical adhesive 41 can be providedover the reflective surface 40 and covered by the phase shifting film42.

The size of the phase shifting optic 32 can be, in one embodiment,larger than the beam splitter. For example, dimensions of the phaseshifting optic 32 can be 11 inches long by 7 inches tall. However, othersizes are possible, including using a phase shifting optic 32 with thesame dimensions as the beam splitter. The size of the phase shiftingoptic 32 can be dependent on a total light path distance from aprojector lens focal point to the phase shifting optic and a desiredminimum width/distance throw ratio for the stereoscopic recyclingdevice.

Further, when positioned within the chassis, the phase shifting optic 32can have a surface shape that is adjustable or static, or a combinationof adjustable and static capabilities as described in further detailbelow. An adjustable phase shifting optic can be adjusted whilepositioned within the chassis, while a static phase shifting optic'ssurface shape can include a free-form mirror that is generated prior toaffixing the phase shifting optic to the chassis.

FIG. 4A is a block diagram showing an adjustable phase shifting optic 32of FIG. 2 moveably connected to the chassis. The phase shifting optic 32is aligned with the top side of the chassis 30 a. A plurality of screws33 are each inserted through at least a portion of the phase shiftingoptic 32 at different locations and extend through the top side of thechassis until exiting on an outer surface of the top side. A nut 50 orother fastener is fastened to the screw on the outer top surface.Alternatively, a head of the screw 33 can be affixed to the phaseshifting optic 32, extend through the top side of the chassis, and exitan outer surface of the top side. The phase shifting optic 32 and topside of the chassis can be located at a distance from one another,leaving a middle portion 51 of the screws exposed. The distance can bedifferent across the phase shifting optic and is dependent uponadjustment necessary to align the images of the two light paths.

A user can manually adjust the phase shifting optic 32 throughcounter-clockwise adjustment of at least a portion of the screws, whichpulls the phase shifting optic nearest the adjusted screws closertowards the top side of the chassis, and through clockwise adjustment ofthe screws, which pushes the phase shifting optic away from the topside. Thus, when the screws are adjusted counter-clockwise, thedistances between the phase shifting optic and top side of the chassisare smaller than when the screws are adjusted clockwise. FIG. 4B is across-sectional view of the phase shifting optic of FIG. 2. A screw 33is affixed to at least a portion of the phase shifting optic 32, whichincludes the reflective surface 40, optical adhesive 41, and phaseshifting film 42. The top side of the chassis 30 a is positioned adistance from the phase shifting optic 32 and the screws 33 extend fromthe phase shifting optic through the top side. A nut 50 or otherfastener is used to hold the screw in place to lock the adjustedalignment. Other means for adjusting the phase shifting optic arepossible. The screws can be adjustable via adjustment knobs using ascrewdriver, a user's hand, or a machine that rotates screws. In oneembodiment, the phase shifting optic 32 can be further globally adjustedby affixing the phase shifting optic to an adjustment device which caninclude a kinematic mount with 2-axis angle adjustments, such as pitchand roll.

To ensure the components of the chassis remain clean, a cover can beaffixed to the back of the chassis to minimize dust or other foreignobjects from building on the beam splitter and phase shifting optic.FIG. 5 is a block diagram showing a back side of the light converter ofFIG. 2. The cover 56 can be sized to enclose the back of the chassis andcan be made from metal, heavy plastic, carbon fiber, wood, or othertypes of materials. The cover 56 can be affixed to the sides of thechassis via screws, nails, glue, or other type of adhesive. A cutout 57can be formed within the back cover to allow light from the projector toenter the light converter. The cutout 57 can be covered byanti-reflective glass or other light-transmissive optical materials, orremain open.

Multiple adjustments 54 for an adjustment device affixed to the chassiscan be presented through the cover 56. To assist in closely aligning theimages from the two light paths, the adjustment device can include akinematic mount with 2-axis angle adjustment such as pitch and roll thatallows the phase shifting optic to be steered vertically andhorizontally, and can further include z-axis translation. Alternatively,or in addition, the beam splitter can be mounted to an adjustment deviceto assist in directing the reflected path image for precise alignment.

As well, a handle 58 can be attached to each of the left and right sidesof the chassis to allow users to easily move the light converter infront of and away from a projector. Additionally, adjustable feet 59 canbe affixed to a bottom surface of the bottom side of the chassis andused to position the light converter in front of the projector.

While the light converter has been described above with an adjustablephase shifting optic, a static phase shifting optic with a uniform ornon-uniform reflective surface shape that is formed prior to placementin the chassis can also be utilized. FIG. 6 is a block diagram showingan alternate light converter 20 with a static phase shifting optic foruse in the recycling device of FIG. 1. A chassis having top 60 a, bottom60 b, left 60 c, and right 60 d sides can house a beam splitter 61 and astatic phase shifting optic 62. The sides of the chassis form front andback openings, which can be enclosed by front 65 and back 66 sides (notshown) each having an opening or aperture (not shown). The beam splitter61 is positioned at an angle within the chassis with the input sidefacing the opening in the back side. The beam splitter 61 can be affixedto the chassis or support members 64 within the chassis, depending on asize of the beam splitter. For instance, when smaller than the distancebetween the left 60 c and right 60 d sides of the chassis, the beamsplitter 61 can be affixed to the support members 64, which areperpendicularly affixed to the bottom side of the chassis. The supportmembers 64 are spaced to accommodate the longest dimension of the beamsplitter 61, while the shorter sides of the beam splitter 61 are affixedto the support members 64. Other sizes and shapes of the beam splitterand the support members are possible, including a circular beam splitterand a cylindrical support member.

The static phase shifting optic 62 is placed at an angle within thechassis above the beam splitter 61 and faces the opening in the frontside. The angle of the phase shifting optic 62 should be in opticalalignment with the beam splitter 62 to provide a clear sharp image byclosely aligning the images from the two light paths. Positioning of thephase shifting optic 62 and beam splitter 61 can be dependent on thesurface of the phase shifting optic and a distance between the projectorand screen, as described infra.

A surface of the static phase shifting optic can have a uniform ornon-uniform shape. The static phase shifting optic can include afree-form mirror and a phase shifting film. A non-uniform,non-rotationally symmetric surface shape for the free-form mirror isdesigned using computer ray-tracing simulations. A required surface isbased on the mathematical description of a higher order xy-polynomial,and a physical surface can be manufactured using ultra-precisioncomputer-controlled machining with tolerances in the sub-micron range.In one instance an inverted master mold is made of the required shapeand glass thermal forming processes including compression molding andthermal slumping are used to economically create subsequent copies fromthe master mold.

As described above with reference to FIGS. 3A and 3B, the phase shiftingfilm can be affixed to the free-form mirror using optical adhesive orother types of adhesive. The free-form mirror can have a non-uniformcurvature whose shape is computer generated. The shape of the free-formmirror is dependent upon a distance between the projector and screen andthe difference in distances between the two light paths within the lightconverter, and serves to align the images of the two light pathways onthe screen. The static phase shifting optic can optionally be placed onone or more adjustment devices used to adjust angle and optionallyposition of the free-form mirror to assist in closely aligning theimages from the two light paths.

Once generated, the surface of the free-form mirror may not be able tobe significantly changed. If a significantly different reflectivesurface of the free-form mirror is required, a new mirror must begenerated and installed. For instance, a particular free-form mirror maybe used with the recycling device for a particular range of throw-ratioswith respect to the projector and projection screen. A different phaseshifting optic with a different free-form mirror may be used with therecycling device when a projector/screen throw-ratio relationship islocated outside a valid throw-ratio range for the current free-formmirror. In one embodiment, a preformed set of phase shifting optics withdifferent free-form mirrors for different ranges of valid throw ratioranges can be generated and provided to a user with the light converter.Based on the distance of the projector from the screen and the size ofthe screen, the user can select an appropriate phase shifting optic andinsert the phase shifting optic within the chassis.

The phase shifting optic can be mounted along an inner surface of thetop side of the chassis or alternatively, the phase shifting optic canbe mounted to the right and left sides of the chassis. Further, thephase shifting optic can be mounted to an adjustment device which ismounted to the chassis. When the phase shifting optic is affixed to thechassis sides, no top side is necessary. Regardless of being placedalong the top side, mounted to the left and right sides, or mounted onan adjustment plate, the static phase shifting optic can be placed upona mount, shelf, or other support mechanism attached to the chassis sothat the static phase shifting optic can be easily changed should adifferent phase shifting optic be required to project images on a screenlocated further or closer to the projector. However, some free-formmirrors may be at least partially adjustable and can be deformed in realtime as described above with reference to the adjustable phase shiftingoptic.

In addition to the light converter, the recycling device includes apolarizing modulator. FIG. 7 is a block diagram showing a side view ofthe recycling device of FIG. 1. A light converter 20 is positioned infront of a lens 19 of a light projector 11 and can be affixed directlyto the light projector, to a stand of the light projector, or to astand, wall or shelf in front of the projector. The light converter 20includes a beam splitter 31 which is positioned at an angle facing thelens and a phase shifting optic 32, which is located above the beamsplitter 31 at an angle facing away from the lens. In a furtherembodiment, the phase shifting optic can be located below the beamsplitter. The beam splitter 31 and phase shifting optic 32 are inoptical alignment, as further described below with reference to FIG. 9.

A polarizing modulator 21 is placed in front of the light converter 20,opposite the light projector 11, and can be affixed to the lightconverter 20 or separately provided. In one embodiment, the recyclingdevice can be affixed to a moveable mount 18 allowing the entirerecycling device to be moved in or out of the projector's light path.Alternatively, only the polarizing modulator 21 can be affixed to amoveable mount, which moves the polarizing modulator back and forth,right and left, or up and down in relation to the lens of the projectorallowing the polarizing modulator to be moved in or out of theprojector's light path.

The polarizing modulator includes a frame, optical window, and controlunit. FIG. 8 is a block diagram showing a front view of the recyclingdevice 13 of FIG. 1. The polarizing modulator 21 is located on a frontside of the light converter 20 and includes an optical window 67surrounded by a frame 68. A control unit can be plugged into the frame68 or into a panel (not shown) that is affixed to the frame. Thepolarizing modulator 21 receives light from the light converter 20 andelectronically switches a polarization orientation of the light passingthrough the modulator by circularly polarizing left and right eye viewsin sync with a digital projector. In one embodiment, the optical window67 of the polarizing modulator is large enough to receive light beamsfrom both the beam splitter and phase shifting optic. In a furtherembodiment, multiple polarizing modulators can be used to receive lightfrom one of the pathways.

Together, the light converter 20 and polarizing modulator 21 form therecycling device 13, which is placed in front of a projector 11displaying alternating left and right stereoscopic images, and used togenerate two common stereoscopic images that are displayed assubstantially overlapping on a projection screen 12. FIG. 9 is a blockdiagram showing, by way of example, light 70 transmitted through therecycling device 13 of FIG. 1. A projector lens emits a single beam ofpartially polarized light 70 towards the beam splitter, which splits thelight beam into two separate paths 71, 72. One path 71 includesp-polarized light that travels along the path of the original light beam70 and passes through the beam splitter 31 to the polarizing modulator21. The polarizing modulator 21 converts the p-polarized light 71 toalternating handedness of circular light in sync with the projected leftand right images, which is projected upon the projection screen and astereoscopic image is displayed.

Meanwhile the light of the other path 72 is directed away from the beamsplitter 31 as s-polarized light. Specifically, the s-polarized light 72is directed towards the phase shifting optic 32, which receives thes-polarized light 72, converts the s-polarized light to p-polarizedlight, and reflects the converted p-polarized light 72 along a path thatis nearly parallel to the p-polarized light that passes through the beamsplitter 31. The converted p-polarized light 72 is transmitted throughthe polarizing modulator 21, which converts the converted p-polarizedlight path 72 to alternating handedness of circular light in sync withthe projected left and right images. The circular light is projected onthe screen 12 where a further stereoscopic image is displayed inrelation to the stereoscopic image of the original p-polarized lightpath 71.

The two stereoscopic images should be closely aligned to provide viewerswith a sharp representation of the 3D image. In one embodiment, 99.9% ofthe images should be aligned. However, other values are possible. Bothsurface shape adjustment of the phase shifting optic, as well aspositioning of the beam splitter and phase shifting optic are importantin providing aligned images. For example, without surface shapeadjustment of the phase shifting optic, a phase shifting optic alignedperfectly parallel to the beam splitter will cause the image directed tothe screen by the phase shifting optic to be larger and higher on theprojection screen relative to the image passed through the beamsplitter. Simply steering the phase shifting optic without surface shapeadjustment so that the center of each image converges on the projectionscreen, the top image will still be too large and keystone distortionwill be introduced so that the bottom of the top image becomes wider andthe sides are no longer parallel. Only adequate surface shapeadjustment, either through adjustable-deformation or static free-formdeformation of the phase shifting optic, in addition to correct opticalalignment of both the beam splitter and the phase shifting optic, willresult in magnification and keystone distortion being minimized with asubstantial image overlap at the screen.

Once both alternating polarized stereoscopic images are overlapped anddisplayed on the polarization preserving screen, viewers wearingmatching passive 3D glasses will benefit from the substantially brighter3D effect of image depth. The lenses of the glasses have differentpolarizations for the right and left eyes so images with onepolarization enter one eye and images with a different polarizationenter the other eye. Subsequently, the viewers' brains can combine theimages received to form a 3D image.

Alternative embodiments of the light converter are possible. FIG. 10 isa block diagram showing the light converter of FIG. 6 with a fixed focallength lens. The fixed focal length lens 75 can be a single lens, suchas a biconvex, plano-convex, plano-concave, biconcave or convex-concavesimple lens, which is positioned within the chassis between the beamsplitter 61 and the phase shifting optic 62. Specifically, the fixedfocal length lens 75 can be horizontally positioned above the supportmembers 64 of the beam splitter 61 and in one example, can be affixed tothe top surface of the support members. In this embodiment, a singleprotective housing of anti-reflection coated glass or light transmissiveoptical material can enclose both the beam splitter and fixed focallength lens. In a further example, the fixed focal length lens can behorizontally affixed to the inner sides of the chassis, between the beamsplitter and phase shifting optic and a separate protective housing canenclose the fixed focal length lens.

The difference in path length between the two beam paths generatedwithin the light converter can cause a slight amount of defocusing inthe image from one path when the image from the other path is focusedsharply. Placement of the fixed focal length lens between the beamsplitter and phase shifting optic can keep the original image pathsharply focused and correct the slight defocusing in the longer paththrough a center of the fixed focal length lens. In a furtherembodiment, at least two lenses could be used in combination to allowslight focus adjustments and to correct for chromatic and sphericalaberrations. Alternately, the lens or lenses can be placed verticallyafter the phase shifting optic and affixed to the chassis (not shown) orin the case of multiple lenses split in location with at least one lensbefore and at least one after the phase shifting optic.

An alternate use of the single fixed focal length lens 75 can be toadjust for the slight magnification difference caused by the slightlylonger path length, while ignoring the small focus difference. Inaddition to the magnification correction, the small amount of keystonedistortion introduced in the longer path can be minimized through asmall off-center shift in position of the fixed focal length lensperpendicular in one axis to the light rays passing through it. Thisshift can either be built into the lens shape, or the lens can beaffixed to a single axis translation stage to enable user adjustment,and the single axis translation stage can be affixed to the chassis orthe top surface of the beam splitter support members 64. The size of thefixed focal length lens 75 can be dependent on a total light pathdistance from a projector lens focal point to the fixed focal lengthlens and a desired minimum width/distance throw ratio for thestereoscopic recycling device.

A different fixed focal length lens may be required for different rangesof throw ratios. For instance, a particular fixed focal length lens maybe used with the recycling device for a particular range of throw-ratioswith respect to the projector and projection screen. A different fixedfocal length lens may be used with the recycling device when aprojector/screen throw-ratio relationship is located outside a validthrow-ratio range for the current fixed focal length lens 75. In oneembodiment, a preformed set of fixed focal length lenses can be createdand provided to a user with the light converter. Based on the distanceof the projector from the screen and the size of the screen, the usercan select an appropriate fixed focal length lens and insert the lenswithin the chassis.

In yet a further embodiment, the light converter can include a telephotolens to correct a magnification difference of the images produced by thetwo light beams. FIG. 11 is a block diagram showing the light converterof FIG. 6 with a telephoto lens pair 80 a-b. Each lens in the pair caninclude additional lenses to correct for aberrations such as chromaticand spherical aberrations. The telephoto lens pair 80 a-b is positionedafter the beam splitter 61, facing the front of the light converter, andcan be affixed to the support members 64 or separately affixed to thechassis. The telephoto lens 80 a-b can correct a magnificationdifference of the images from the two light beams generated by the lightconverter. Generally, the images of one of the paths are larger sincethe light beam travels a longer path than the other light beam.Placement of the telephoto lens pair 80 a-b after the beam splitter 61can increase magnification of the image from the light beam along theshorter path. Meanwhile, any keystone distortion created in the longerreflected path can be allowed to remain uncorrected, can be minimizedthrough a small shift in position of at least one of the lenses along anaxis perpendicular to the light path, or can be separately adjustedusing either the adjustable or static phase shifting optic.

A still further embodiment provides a light converter with a four-prismcube beam splitter. FIG. 12 is a block diagram 90 showing light 93transmitted through the recycling device 13 of FIG. 1 with a four-prismcube beam splitter 91 to create two equal path lengths. In thisembodiment, two separate substantially orthogonally polarized pathwaysof light 94, 95 exit the cube beam splitter in opposite directions. Onepath 95 is directed to the phase shifting optic 32, while the other 94is directed to a reflector 92 located in the housing opposite the phaseshifting optic. For example, referring back to the light converter ofFIG. 2, the reflector 92 can be positioned below the beam splitter. Thereflector can be affixed to an adjustment device which is affixed to thechassis to assist in closely aligning the images from the two lightpaths. The adjustment device can include a kinematic mount with 2-axisangle adjustment such as pitch and roll that allows the reflector to besteered vertically and horizontally, and can further include z-axistranslation. Use of the four-prism cube beam splitter creates nomagnification or focus difference, thus requires no magnification orfocus correction. Keystone distortion is still introduced and can becorrected using either the adjustable or static phase shifting optic, orallowed to remain uncorrected.

A further embodiment provides a recycling device with a dual beamsplitter. FIG. 13 is a block image showing the light transmitted throughthe recycling device 13 of FIG. 1 with two beam splitters 101, 102 andtwo phase shifting optics 32. A dual beam splitter is positioned withinthe light converter of the recycling device and includes the two beamsplitters 101, 102 that are arranged to form an angle. The vertex of theangle faces the projector, while an input side of each beam splitteralso faces the projector. Phase shifting optics 32 are located onopposite sides of the dual beam splitter 101, 102.

The projector emits a beam of partially polarized light towards the dualbeam splitters 32, which split the light beam into three separate paths.One path includes p-polarized light that travels along the path of theoriginal light beam and passes through the dual beam splitter to apolarizing modulator 21. The polarizing modulator 21 converts thep-polarized light to alternating handedness of circular light in syncwith the projected left and right images, which is projected upon theprojection screen and a stereoscopic image is displayed.

Meanwhile, light is directed away from each of the beam splitters 101,102 in opposite directions as s-polarized light. Specifically, thes-polarized light is directed towards the respective phase shiftingoptic 32, which receives the s-polarized light, converts the s-polarizedlight to p-polarized light, and reflects the converted p-polarized lightalong a path that is nearly parallel to the p-polarized light thatpasses through the beam splitter. The converted p-polarized light istransmitted through the polarizing modulator 21, which converts theconverted p-polarized light path to alternating handedness of circularlight in sync with the projected left and right images. The circularlight is projected on the screen where a further stereoscopic image isdisplayed in relation to the stereoscopic image of the originalp-polarized light path.

A surface of the phase shifting optic can have a uniform or non-uniformshape which can depend on the intended type and amount of imagecorrection to be created by the phase shifting optic in order to achievesubstantial image overlap at the screen. FIG. 14A is a ray traceshowing, in one example, the light reflected away from the static phaseshifting optic 62 of FIG. 6 having a uniform flat shape, while FIG. 14Bis a ray trace showing, in one example, the light reflected away fromthe adjustable phase shifting optic 32 of FIG. 2, with an exaggeratedadjustment to illustrate a type of non-uniform surface shape possible.FIG. 14C is a ray trace showing, in one example, the light reflectedaway from a static phase shifting optic 63 but with an exaggeratedpre-formed non-uniform surface shape.

While the invention has been particularly shown and described asreferenced to the embodiments thereof, those skilled in the art willunderstand that the foregoing and other changes in form and detail maybe made therein without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A stereoscopic device for recapturing light,comprising: a chassis open to light in front and back forming a housingthat frames the front and back openings; a beam splitter constructed ofsubstantially orthogonally polarizing material facing the back openingand captively held to the chassis; a single phase shifting opticcomprising a reflective surface coated by a phase shifting film andangled toward the front opening, wherein the beam splitter and phaseshifting optic are in optical alignment with each other within thechassis; and a modulator sized to cover at least a portion of the frontopening and positioned in front of the front opening.
 2. A stereoscopicdevice according to claim 1, wherein the chassis is positioned in frontof a digital projector such that an input side of the beam splitterfaces a lens of the projector.
 3. A stereoscopic device according toclaim 1, wherein the reflective surface of the phase shifting opticcomprises a free-form mirror.
 4. A stereoscopic device according toclaim 1, wherein the reflective surface of the phase shifting opticcomprises an adjustable mirror.
 5. A stereoscopic device according toclaim 1, wherein the phase shifting film of the phase shifting opticcomprises quarter wave retarder film.
 6. A stereoscopic device accordingto claim 1, wherein the phase shifting film of the phase shifting opticis affixed to the reflective surface via at least one of opticaladhesive and direct coating.
 7. A stereoscopic device according to claim1, further comprising at least one of: a static support structureaffixed to the chassis and configured to support the beam splitter at afixed angle; and an adjustable support structure affixed to the chassisand configured to support the beam splitter at adjustable angles.
 8. Astereoscopic device according to claim 1, wherein the phase shiftingoptic is affixed to the chassis via one of the top side and the twosides.
 9. A stereoscopic device according to claim 1, furthercomprising: an adjustment device affixed to the chassis and configuredto support the phase shifting optic at adjustable angles.
 10. Astereoscopic device according to claim 1, further comprising: a furtherphase shifting optic that is interchangeable with the phase shiftingoptic.
 11. A stereoscopic device according to claim 1, furthercomprising at least one of: a fixed-focus lens positioned between thebeam splitter and the phase shifting optic; and a fixed-focus lenspositioned after the beam splitter and the phase shifting optic.
 12. Astereoscopic device according to claim 1, further comprising at leastone of: a plurality of lenses positioned in a light path between thebeam splitter and the modulator; and a plurality of lenses positioned ina light path after the beam splitter and the modulator.
 13. Astereoscopic device according to claim 1, further comprising: a furthermodulator positioned to separately receive light from one of the beamsplitter and light from the phase shifting optic.
 14. A stereoscopicdevice according to claim 1, wherein the beam splitter is at least oneof a wire grid polarizer, a two-prism polarizing cube beam splitter, anda four-prism polarizing X prism cube beam splitter.
 15. A stereoscopicdevice according to claim 1, further comprising: a reflector positionedopposite the phase shifting optic in relation to the beam splitter, andangled toward the front opening, wherein the reflector and the beamsplitter are in optical alignment with each other within the chassis.16. A stereoscopic device according to claim 15, further comprising: anadjustment device affixed to the chassis and configured to support thereflector at adjustable angles.
 17. A stereoscopic device according toclaim 1, further comprising: a further beam splitter affixed at an angleto the beam splitter as a dual beam splitter.
 18. A stereoscopic deviceaccording to claim 1, further comprising: a protective housing toseparately enclose at least one of the beam splitter and the phaseshifting optic.
 19. A stereoscopic device according to claim 1, furthercomprising: a back panel to cover the back opening of the chassis; and awindow formed within the back panel.
 20. A stereoscopic device accordingto claim 19, further comprising: a substantially non-reflective lighttransmissive material to cover the window in the back panel.
 21. Astereoscopic device according to claim 11, further comprising: a furtherfixed-focus lens that is interchangeable with the fixed-focus lens. 22.A stereoscopic device according to claim 11, further comprising: anadjustment device affixed to one of the beam splitter support and thechassis and configured to support and translate the fixed-focus lensalong a single axis.